Hierarchical memory systems

ABSTRACT

Apparatuses, systems, and methods for hierarchical memory systems are described. A hierarchical memory system can leverage persistent memory to store data that is generally stored in a non-persistent memory, thereby increasing an amount of storage space allocated to a computing system at a lower cost than approaches that rely solely on non-persistent memory. An example method includes receiving an interrupt message by a hypervisor, the interrupt message generated by a hierarchical memory component responsive to receiving a read request initiated by an input/output (I/O) device, gathering, by the hypervisor, address register access information from the hierarchical memory component, and determining, by the hypervisor, a physical location of data associated with the read request.

PRIORITY INFORMATION

This application is a continuation of U.S. application Ser. No.16/548,286, filed Aug. 22, 2019, the contents of which are incorporatedherein by reference.

TECHNICAL FIELD

The present disclosure relates generally to semiconductor memory andmethods, and more particularly, to apparatuses, systems, and methodsrelated to hierarchical memory systems.

BACKGROUND

Memory devices are typically provided as internal, semiconductor,integrated circuits in computers or other electronic systems. There aremany different types of memory including volatile and non-volatilememory. Volatile memory can require power to maintain its data (e.g.,host data, error data, etc.) and includes random access memory (RAM),dynamic random access memory (DRAM), static random access memory (SRAM),and synchronous dynamic random access memory (SDRAM), among others.Non-volatile memory can provide persistent data by retaining stored datawhen not powered and can include NAND flash memory, NOR flash memory,and resistance variable memory such as phase change random access memory(PCRAM), resistive random access memory (RRAM), and magnetoresistiverandom access memory (MRAM), such as spin torque transfer random accessmemory (STT RAM), among others.

Memory devices may be coupled to a host (e.g., a host computing device)to store data, commands, and/or instructions for use by the host whilethe computer or electronic system is operating. For example, data,commands, and/or instructions can be transferred between the host andthe memory device(s) during operation of a computing or other electronicsystem.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram in the form of an apparatusincluding a hierarchical memory component in accordance with a number ofembodiments of the present disclosure.

FIG. 2 is a functional block diagram in the form of a computing systemincluding a hierarchical memory component in accordance with a number ofembodiments of the present disclosure.

FIG. 3 is another functional block diagram in the form of a computingsystem including a hierarchical memory component in accordance with anumber of embodiments of the present disclosure.

FIG. 4 is a flow diagram representing a data read operation inaccordance with a number of embodiments of the present disclosure.

FIG. 5 is a flow diagram representing a data write operation inaccordance with a number of embodiments of the present disclosure.

FIG. 6 is a flow diagram representing an example method for ahierarchical memory system in accordance with a number of embodiments ofthe present disclosure.

FIG. 7 is another flow diagram representing an example method for ahierarchical memory system in accordance with a number of embodiments ofthe present disclosure.

DETAILED DESCRIPTION

Apparatuses, systems, and methods for hierarchical memory systems aredescribed. A hierarchical memory system can leverage persistent memoryto store data that is generally stored in a non-persistent memory,thereby increasing an amount of storage space allocated to a computingsystem at a lower cost than approaches that rely solely onnon-persistent memory. An example method includes receiving a request toaccess data via an input/output (I/O) device, determining whether thedata is stored in a non-persistent memory device or a persistent memorydevice, and redirecting the request to access the data to logiccircuitry in response to determining that the data is stored in thepersistent memory device.

Computing systems utilize various types of memory resources duringoperation. For example, a computing system may utilize a combination ofvolatile (e.g., random-access memory) memory resources and non-volatile(e.g., storage) memory resources during operation. In general, volatilememory resources can operate at much faster speeds than non-volatilememory resources and can have longer lifespans than non-volatile memoryresources; however, volatile memory resources are typically moreexpensive than non-volatile memory resources. As used herein, a volatilememory resource may be referred to in the alternative as a“non-persistent memory device” while a non-volatile memory resource maybe referred to in the alternative as a “persistent memory device.”

However, a persistent memory device can more broadly refer to theability to access data in a persistent manner. As an example, in thepersistent memory context, the memory device can store a plurality oflogical to physical mapping or translation data and/or lookup tables ina memory array in order to track the location of data in the memorydevice, separate from whether the memory is non-volatile. Further, apersistent memory device can refer to both the non-volatility of thememory in addition to using that non-volatility by including the abilityto service commands for successive processes (e.g., by using logical tophysical mapping, look-up tables, etc.).

These characteristics can necessitate trade-offs in computing systems inorder to provision a computing system with adequate resources tofunction in accordance with ever-increasing demands of consumers andcomputing resource providers. For example, in a multi-user computingnetwork (e.g., a cloud-based computing system deployment, a softwaredefined data center, etc.), a relatively large quantity of volatilememory may be provided to provision virtual machines running in themulti-user network. However, by relying on volatile memory to providethe memory resources to the multi-user network, as is common in someapproaches, costs associated with provisioning the network with memoryresources may increase, especially as users of the network demand largerand larger pools of computing resources to be made available.

Further, in approaches that rely on volatile memory to provide thememory resources to provision virtual machines in a multi-user network,once the volatile memory resources are exhausted (e.g., once thevolatile memory resources are allocated to users of the multi-usernetwork), additional users may not be added to the multi-user networkuntil additional volatile memory resources are available or added. Thiscan lead to potential users being turned away, which can result in aloss of revenue that could be generated if additional memory resourceswere available to the multi-user network.

Volatile memory resources, such as dynamic random-access memory (DRAM)tend to operate in a deterministic manner while non-volatile memoryresources, such as storage class memories (e.g., NAND flash memorydevices, solid-state drives, resistance variable memory devices, etc.)tend to operate in a non-deterministic manner. For example, due to errorcorrection operations, encryption operations, RAID operations, etc. thatare performed on data retrieved from storage class memory devices, anamount of time between requesting data from a storage class memorydevice and the data being available can vary from read to read, therebymaking data retrieval from the storage class memory devicenon-deterministic. In contrast, an amount of time between requestingdata from a DRAM device and the data being available can remain fixedfrom read to read, thereby making data retrieval from a DRAM devicedeterministic.

In addition, because of the distinction between the deterministicbehavior of volatile memory resources and the non-deterministic behaviorof non-volatile memory resources, data that is transferred to and fromthe memory resources generally traverses a particular interface (e.g., abus) that is associated with the type of memory being used. For example,data that is transferred to and from a DRAM device is typically passedvia a double data rate (DDR) bus, while data that is transferred to andfrom a NAND device is typically passed via a peripheral componentinterconnect express (PCI-e) bus. As will be appreciated, examples ofinterfaces over which data can be transferred to and from a volatilememory resource and a non-volatile memory resource are not limited tothese specific enumerated examples, however.

Because of the different behaviors of non-volatile memory device andvolatile memory devices, some approaches opt to store certain types ofdata in either volatile or non-volatile memory. This can mitigate issuesthat can arise due to, for example, the deterministic behavior ofvolatile memory devices compared to the non-deterministic behavior ofnon-volatile memory devices. For example, computing systems in someapproaches store small amounts of data that are regularly accessedduring operation of the computing system in volatile memory deviceswhile data that is larger or accessed less frequently is stored in anon-volatile memory device. However, in multi-user network deployments,the vast majority of data may be stored in volatile memory devices. Incontrast, embodiments herein can allow for data storage and retrievalfrom a non-volatile memory device deployed in a multi-user network.

As described herein, some embodiments of the present disclosure aredirected to computing systems in which data from a non-volatile, andhence, non-deterministic, memory resource is passed via an interfacethat is restricted to use by a volatile and deterministic memoryresource in other approaches. For example, in some embodiments, data maybe transferred to and from a non-volatile, non-deterministic memoryresource, such as a NAND flash device, a resistance variable memorydevice, such as a phase change memory device and/or a resistive memorydevice (e.g., a three-dimensional Crosspoint (3D XP) memory device), asolid-state drive (SSD), a self-selecting memory (SSM) device, etc. viaan interface such as a DDR interface that is reserved for data transferto and from a volatile, deterministic memory resource in someapproaches. Accordingly, in contrast to approaches in which volatile,deterministic memory devices are used to provide main memory to acomputing system, embodiments herein can allow for non-volatile,non-deterministic memory devices to be used as at least a portion of themain memory for a computing system.

In some embodiments, the data may be intermediately transferred from thenon-volatile memory resource to a cache (e.g., a small staticrandom-access memory (SRAM) cache) or buffer and subsequently madeavailable to the application that requested the data. By storing datathat is normally provided in a deterministic fashion in anon-deterministic memory resource and allowing access to that data asdescribed herein, computing system performance may be improved by, forexample, allowing for a larger amount of memory resources to be madeavailable to a multi-user network at a substantially reduced cost incomparison to approaches that operate using volatile memory resources.

In order to facilitate embodiments of the present disclosure, visibilityof the non-volatile memory resources to various devices of the computingsystem in which the hierarchical memory system is deployed may beobfuscated. For example, host(s), network interface card(s), virtualmachine(s), etc. that are deployed in the computing system or multi-usernetwork may be unable to distinguish between whether data is stored by avolatile memory resource or a non-volatile memory resource of thecomputing system. For example, hardware circuitry may be deployed in thecomputing system that can register addresses that correspond to the datain such a manner that the host(s), network interface card(s), virtualmachine(s), etc. are unable to distinguish whether the data is stored byvolatile or non-volatile memory resources.

As described in more detail herein, a hierarchical memory system mayinclude hardware circuitry (e.g., logic circuitry) that can interceptredirected data requests, register an address in the logic circuitryassociated with the requested data (despite the hardware circuitry notbeing backed up by its own memory resource to store the data), and map,using the logic circuitry, the address registered in the logic circuitryto a physical address corresponding to the data in a non-volatile memorydevice.

In the following detailed description of the present disclosure,reference is made to the accompanying drawings that form a part hereof,and in which is shown by way of illustration how one or more embodimentsof the disclosure may be practiced. These embodiments are described insufficient detail to enable those of ordinary skill in the art topractice the embodiments of this disclosure, and it is to be understoodthat other embodiments may be utilized and that process, electrical, andstructural changes may be made without departing from the scope of thepresent disclosure.

As used herein, designators such as “N,” “M,” etc., particularly withrespect to reference numerals in the drawings, indicate that a number ofthe particular feature so designated can be included. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting. As used herein, the singular forms “a,” “an,” and “the” caninclude both singular and plural referents, unless the context clearlydictates otherwise. In addition, “a number of,” “at least one,” and “oneor more” (e.g., a number of memory banks) can refer to one or morememory banks, whereas a “plurality of” is intended to refer to more thanone of such things.

Furthermore, the words “can” and “may” are used throughout thisapplication in a permissive sense (i.e., having the potential to, beingable to), not in a mandatory sense (i.e., must). The term “include,” andderivations thereof, means “including, but not limited to.” The terms“coupled” and “coupling” mean to be directly or indirectly connectedphysically or for access to and movement (transmission) of commandsand/or data, as appropriate to the context. The terms “data” and “datavalues” are used interchangeably herein and can have the same meaning,as appropriate to the context.

The figures herein follow a numbering convention in which the firstdigit or digits correspond to the figure number and the remaining digitsidentify an element or component in the figure. Similar elements orcomponents between different figures may be identified by the use ofsimilar digits. For example, 104 may reference element “04” in FIG. 1 ,and a similar element may be referenced as 204 in FIG. 2 . A group orplurality of similar elements or components may generally be referred toherein with a single element number. For example, a plurality ofreference elements 106-1, 106-2, . . . , 106-N (e.g., 106-1 to 106-N)may be referred to generally as 106. As will be appreciated, elementsshown in the various embodiments herein can be added, exchanged, and/oreliminated so as to provide a number of additional embodiments of thepresent disclosure. In addition, the proportion and/or the relativescale of the elements provided in the figures are intended to illustratecertain embodiments of the present disclosure and should not be taken ina limiting sense.

FIG. 1 is a functional block diagram in the form of a computing system100 including an apparatus including a hierarchical memory component 104in accordance with a number of embodiments of the present disclosure. Asused herein, an “apparatus” can refer to, but is not limited to, any ofa variety of structures or combinations of structures, such as a circuitor circuitry, a die or dice, a module or modules, a device or devices,or a system or systems, for example. In some embodiments, thehierarchical memory component 104 can be provided as a fieldprogrammable gate array (FPGA), application-specific integrated circuit(ASIC), a number of discrete circuit components, etc., and can bereferred to herein in the alternative as “logic circuitry.”

The hierarchical memory component 104 can, as illustrated in FIG. 1 ,include a memory resource 102, which can include a read buffer 103, awrite buffer 105, and/or an input/output I/O device access component107. In some embodiments, the memory resource 102 can be a random-accessmemory resource, such as a block RAM, which can allow for data to bestored within the hierarchical memory component 104 in embodiments inwhich the hierarchical memory component 104 is a FPGA. However,embodiments are not so limited, and the memory resource 102 can comprisevarious registers, caches, memory arrays, latches, and SRAM, DRAM,EPROM, or other suitable memory technologies that can store data such asbit strings that include registered addresses that correspond tophysical locations in which data is stored external to the logiccircuitry 104. The memory resource 102 is internal to the hierarchicalmemory component 104 and is generally smaller than memory that isexternal to the hierarchical memory component 104, such as persistentand/or non-persistent memory resources that can be external to thehierarchical memory component 104.

The read buffer 103 can include a portion of the memory resource 102that is reserved for storing data that has been received by thehierarchical memory component 104 but has not been processed by thehierarchical memory component 104. In some embodiments, the read buffer103 can be around 4 Kilobytes (KB) in size, although embodiments are notlimited to this particular size. The read buffer 103 can buffer datathat is to be registered in one of the address registers 106-1 to 106-N.

The write buffer 105 can include a portion of the memory resource 102that is reserved for storing data that is awaiting transmission to alocation external to the hierarchical memory component 104. In someembodiments, the write buffer 105 can be around 4 Kilobytes (KB) insize, although embodiments are not limited to this particular size. Thewrite buffer 103 can buffer data that is registered in one of theaddress registers 106-1 to 106-N.

The I/O access component 107 can include a portion of the memoryresource 102 that is reserved for storing data, which may be referred toherein as “I/O device access information,” that corresponds to access toa component external to the hierarchical memory component 104, such asthe I/O device 210/310 illustrated in FIGS. 2 and 3 , herein. The I/Oaccess component 107 can store data corresponding to addresses of theI/O device, which can be used to read and/or write data to and from theI/O device. In addition, the I/O access component 107 can, in someembodiments, receive, store, and/or transmit data corresponding to astatus of a hypervisor (e.g., the hypervisor 312 illustrated in FIG. 3), as described in more detail in connection with FIG. 3 , herein.

The hierarchical memory component 104 can further include a memoryaccess multiplexer (MUX) 109, a state machine 111, and/or a hierarchicalmemory controller 113 (or, for simplicity, “controller”). As shown inFIG. 1 , the hierarchical memory controller 113 can include a pluralityof address registers 106-3 to 106-N and/or an interrupt component 115.The memory access MUX 109 can include circuitry that can comprise one ormore logic gates and can be configured to control data and/or addressbussing for the logic circuitry 104. For example, the memory access MUX109 can transfer messages to and from the memory resource 102, as wellas communicate with the hierarchical memory controller 113 and/or thestate machine 111, as described in more detail below.

In some embodiments, the MUX 109 can redirect incoming messages and/orcommands from a host (e.g., a host computing device, virtual machine,etc.) received to the hierarchical memory component 104. For example,the MUX 109 can redirect an incoming message corresponding to an accessrequest from an input/output (I/O) device (e.g., the I/O device 210/310illustrated in FIGS. 2 and 3 , herein) to one of the address registers(e.g., the address register 106-N, which can be a BAR4 region of thehierarchical memory controller 113, as described below) to the readbuffer 103 and/or the write buffer 105.

In addition, the MUX 109 can redirect requests (e.g., read requests,write requests) received by the hierarchical memory component 104. Insome embodiments, the requests can be received by the hierarchicalmemory component 104 from a hypervisor (e.g., the hypervisor 312illustrated in FIG. 3 , herein), a bare metal server, or host computingdevice communicatively coupled to the hierarchical memory component 104.Such requests may be redirected by the MUX 109 from the read buffer 103,the write buffer 105, and/or the I/O access component 107 to an addressregister (e.g., the address register 106-2, which can be a BAR2 regionof the hierarchical memory controller 113, as described below).

The MUX 109 can redirect such requests as part of an operation todetermine an address in the address register(s) 106 that is to beaccessed. In some embodiments, the MUX 109 can redirect such requests aspart of an operation to determine an address in the address register(s)that is to be accessed in response to assertion of a hypervisorinterrupt (e.g., an interrupt asserted to a hypervisor coupled to thehierarchical memory component 104 that is generated by the interruptcomponent 115).

In response to a determination that the request corresponds to data(e.g., data associated with an address being written to a locationexternal to the hierarchical memory component 104 (e.g., to a persistentmemory device such as the persistent memory device 216/316 illustratedin FIGS. 2 and 3 , herein), the MUX 109 can facilitate retrieval of thedata, transfer of the data to the write buffer 105, and/or transfer ofthe data to the location external to the hierarchical memory component104. In response to a determination that the request corresponds to databeing read from a location external to the hierarchical memory component104 (e.g., from the persistent memory device), the MUX 109 canfacilitate retrieval of the data, transfer of the data to the readbuffer 103, and/or transfer of the data or address informationassociated with the data to a location internal to the hierarchicalmemory component 104, such as the address register(s) 106.

As a non-limiting example, if the hierarchical memory component 104receives a read request from the I/O device, the MUX 109 can facilitateretrieval of data from a persistent memory device via the hypervisor byselecting the appropriate messages to send from the hierarchical memorycomponent 104. For example, the MUX 109 can facilitate generation of aninterrupt using the interrupt component 115, cause the interrupt to beasserted on the hypervisor, buffer data received from the persistentmemory device into the read buffer 103, and/or respond to the I/O devicewith an indication that the read request has been fulfilled. In anon-limiting example in which the hierarchical memory component 104receives a write request from the I/O device, the MUX 109 can facilitatetransfer of data to a persistent memory device via the hypervisor byselecting the appropriate messages to send from the hierarchical memorycomponent 104. For example, the MUX 109 can facilitate generation of aninterrupt using the interrupt component 115, cause the interrupt to beasserted on the hypervisor, buffer data to be transferred to thepersistent memory device into the write buffer 105, and/or respond tothe I/O device with an indication that the write request has beenfulfilled.

The state machine 111 can include one or more processing devices,circuit components, and/or logic that are configured to performoperations on an input and produce an output. In some embodiments, thestate machine 111 can be a finite state machine (FSM) or a hardwarestate machine that can be configured to receive changing inputs andproduce a resulting output based on the received inputs. For example,the state machine 111 can transfer access info (e.g., “I/O ACCESS INFO”)to and from the memory access multiplexer 109, as well as interruptconfiguration information (e.g., “INTERRUPT CONFIG”) and/or interruptrequest messages (e.g., “INTERRUPT REQUEST”) to and from thehierarchical memory controller 113. In some embodiments, the statemachine 111 can further transfer control messages (e.g., “MUX CTRL”) toand from the memory access multiplexer 109.

The ACCESS INFO message can include information corresponding to a dataaccess request received from an I/O device external to the hierarchicalmemory component 104. In some embodiments, the ACCESS INFO can includelogical addressing information that corresponds to data that is to bestored in a persistent memory device or addressing information thatcorresponds to data that is to be retrieved from the persistent memorydevice.

The INTERRUPT CONFIG message can be asserted by the state machine 111 onthe hierarchical memory controller 113 to configure appropriateinterrupt messages to be asserted external to the hierarchical memorycomponent 104. For example, when the hierarchical memory component 104asserts an interrupt on a hypervisor coupled to the hierarchical memorycomponent 104 as part of fulfilling a redirected read or write request,the INTERRUPT CONFIG message can generated by the state machine 111 togenerate an appropriate interrupt message based on whether the operationis an operation to retrieve data from a persistent memory device or anoperation to write data to the persistent memory device.

The INTERRUPT REQUEST message can be generated by the state machine 111and asserted on the interrupt component 115 to cause an interruptmessage to be asserted on the hypervisor (or bare metal server or othercomputing device). As described in more detail herein, the interrupt 115can be asserted on the hypervisor to cause the hypervisor to prioritizedata retrieval or writing of data to the persistent memory device aspart of operation of a hierarchical memory system.

The MUX CTRL message(s) can be generated by the state machine 111 andasserted on the MUX 109 to control operation of the MUX 109. In someembodiments, the MUX CTRL message(s) can be asserted on the MUX 109 bythe state machine 111 (or vice versa) as part of performance of the MUX109 operations described above.

The hierarchical memory controller 113 can include a core, such as anintegrated circuit, chip, system-on-a-chip, or combinations thereof. Insome embodiments, the hierarchical memory controller 113 can be aperipheral component interconnect express (PCIe) core. As used herein, a“core” refers to a reusable unit of logic, processor, and/orco-processors that receive instructions and perform tasks or actionsbased on the received instructions.

The hierarchical memory controller 113 can include address registers106-1 to 106-N and/or an interrupt component 115. The address registers106-1 to 106-N can be base address registers (BARs) that can storememory addresses used by the logic circuitry 104 or a computing system(e.g., the computing system 201/301 illustrated in FIGS. 2 and 3 ,herein). At least one of the address registers (e.g., the addressregister 106-1) can store memory addresses that provide access tointernal registers of the logic circuitry 104 from an external locationsuch as the hypervisor 312 illustrated in FIG. 3 .

A different address register (e.g., the address register 106-2) can beused to store addresses that correspond to interrupt control, asdescribed in more detail herein. In some embodiments, the addressregister 106-2 can map direct memory access (DMA) read and DMA writecontrol and/or status registers. For example, the address register 106-2can include addresses that correspond to descriptors and/or control bitsfor DMA command chaining, which can include the generation of one ormore interrupt messages that can be asserted to a hypervisor as part ofoperation of a hierarchical memory system, as described in connectionwith FIG. 3 , herein.

Yet another one of the address registers (e.g., the address register106-3) can store addresses that correspond to access to and from ahypervisor (e.g., the hypervisor 312 illustrated in FIG. 3 , herein). Insome embodiments, access to and/or from the hypervisor can be providedvia an Advanced eXtensible Interface (AXI) DMA associated with thehierarchical memory component 104. In some embodiments, the addressregister can map addresses corresponding to data transferred via a DMA(e.g., an AXI DMA) of the hierarchical memory component 104 to alocation external to the hierarchical memory component 104.

In some embodiments, at least one address register (e.g., the addressregister 106-N) can store addresses that correspond to I/O device (e.g.,the I/O device 210 illustrated in FIG. 2 ) access to the logic circuitry104. The address register 106-N may store addresses that are bypassed byDMA components associated with the hierarchical memory component 104.The address register 106-N can be provided such that addresses mappedthereto are not “backed up” by a physical memory location of the logiccircuity 104. That is, in some embodiments, the hierarchical memorycomponent 104 can be configured with an address space that storesaddresses that correspond to data stored in a persistent memory device(e.g., the persistent memory device 216 illustrated in FIG. 2 ) and notto data stored by the hierarchical memory component 104. For example,the address register 106-N can be configured as a virtual address spacethat can store logical addresses that correspond to physical memorylocations (e.g., in a memory device) in which data is stored.

In some embodiments, the address register 106-N can include a quantityof address spaces that correspond to a size of a memory device (e.g.,the persistent memory device 216/316 illustrated in FIGS. 2 and 3 ,herein). For example, if the memory device contains one terabyte ofstorage, the address register 106-N can be configured to have an addressspace that can include one terabyte of address space. However, asdescribed above, the address register 106-N does not actually includeone terabyte of storage and instead is configured to appear to have oneterabyte of storage space.

Although not explicitly shown in FIG. 1 , the hierarchical memorycomponent 104 can be coupled to a host computing system. The hostcomputing system can include a system motherboard and/or backplane andcan include a number of processing resources (e.g., one or moreprocessors, microprocessors, or some other type of controllingcircuitry). The host and the apparatus 100 can be, for instance, aserver system and/or a high-performance computing (HPC) system and/or aportion thereof. In some embodiments, the computing system can have aVon Neumann architecture, however, embodiments of the present disclosurecan be implemented in non-Von Neumann architectures, which may notinclude one or more components (e.g., CPU, ALU, etc.) often associatedwith a Von Neumann architecture.

FIG. 2 is a functional block diagram in the form of a computing system201 including a hierarchical memory component 204 (e.g., logiccircuitry) in accordance with a number of embodiments of the presentdisclosure. As shown in FIG. 2 , the computing system 201 can include ahierarchical memory component 204, which can be analogous to thehierarchical memory component 104 illustrated in FIG. 1 . In addition,the computing system 201 can include an input/output (I/O) device 210, apersistent memory device 216, a non-persistent memory device 230, anintermediate memory component 220, and a memory management component214. Communication between the logic circuitry 204, the I/O device 210and the persistent memory device 216, the non-persistent memory device230, and the memory management component 214 may be facilitated via aninterface 208.

The I/O device 210 can be a device that is configured to provide directmemory access via a physical address and/or a virtual machine physicaladdress. In some embodiments, the I/O device 210 can be a networkinterface card (NIC) or network interface controller, a storage device,a graphics rendering device, or other I/O device. The I/O device 210 canbe a physical I/O device or the I/O device 210 can be a virtualized I/Odevice 210. For example, in some embodiments, the I/O device 210 can bea physical card that is physically coupled to a computing system via abus or interface such as a PCIe interface or other suitable interface.In embodiments in which the I/O device 210 is a virtualized I/O device210, the virtualized I/O device 210 can provide I/O functionality in adistributed manner.

The persistent memory device 216 can include a number of arrays ofmemory cells. The arrays can be flash arrays with a NAND architecture,for example. However, embodiments are not limited to a particular typeof memory array or array architecture. The memory cells can be grouped,for instance, into a number of blocks including a number of physicalpages. A number of blocks can be included in a plane of memory cells andan array can include a number of planes.

The persistent memory device 216 can include volatile memory and/ornon-volatile memory. In a number of embodiments, the persistent memorydevice 216 can include a multi-chip device. A multi-chip device caninclude a number of different memory types and/or memory modules. Forexample, a memory system can include non-volatile or volatile memory onany type of a module. In embodiments in which the persistent memorydevice 216 includes non-volatile memory, the persistent memory device216 can be a flash memory device such as NAND or NOR flash memorydevices.

Embodiments are not so limited, however, and the persistent memorydevice 216 can include other non-volatile memory devices such asnon-volatile random-access memory devices (e.g., NVRAM, ReRAM, FeRAM,MRAM, PCM), “emerging” memory devices such as resistance variable memorydevices (e.g., resistive and/or phase change memory devices such as a 3DCrosspoint (3D XP) memory device), memory devices that include an arrayof self-selecting memory (SSM) cells, etc., or combinations thereof. Aresistive and/or phase change array of non-volatile memory can performbit storage based on a change of bulk resistance, in conjunction with astackable cross-gridded data access array. Additionally, in contrast tomany flash-based memories, resistive and/or phase change memory devicescan perform a write in-place operation, where a non-volatile memory cellcan be programmed without the non-volatile memory cell being previouslyerased. In contrast to flash-based memories, self-selecting memory cellscan include memory cells that have a single chalcogenide material thatserves as both the switch and storage element for the memory cell.

The persistent memory device 216 can provide a storage volume for thecomputing system 201 and can therefore be used as additional memory orstorage throughout the computing system 201, main memory for thecomputing system 201, or combinations thereof. Embodiments are notlimited to a particular type of memory device, however, and thepersistent memory device 216 can include RAM, ROM, SRAM DRAM, SDRAM,PCRAM, RRAM, and flash memory, among others. Further, although a singlepersistent memory device 216 is illustrated in FIG. 2 , embodiments arenot so limited, and the computing system 201 can include one or morepersistent memory devices 216, each of which may or may not have a samearchitecture associated therewith. As a non-limiting example, in someembodiments, the persistent memory device 216 can comprise two discretememory devices that are different architectures, such as a NAND memorydevice and a resistance variable memory device.

The non-persistent memory device 230 can include volatile memory, suchas an array of volatile memory cells. In a number of embodiments, thenon-persistent memory device 230 can include a multi-chip device. Amulti-chip device can include a number of different memory types and/ormemory modules. In some embodiments, the non-persistent memory device230 can serve as the main memory for the computing system 201. Forexample, the non-persistent memory device 230 can be a dynamicrandom-access (DRAM) memory device that is used to provide main memoryto the computing system 230. Embodiments are not limited to thenon-persistent memory device 230 comprising a DRAM memory device,however, and in some embodiments, the non-persistent memory device 230can include other non-persistent memory devices such as RAM, SRAM DRAM,SDRAM, PCRAM, and/or RRAM, among others.

The non-persistent memory device 230 can store data that can berequested by, for example, a host computing device as part of operationof the computing system 201. For example, when the computing system 201is part of a multi-user network, the non-persistent memory device 230can store data that can be transferred between host computing devices(e.g., virtual machines deployed in the multi-user network) duringoperation of the computing system 201.

In some approaches, non-persistent memory such as the non-persistentmemory device 230 can store all user data accessed by a host (e.g., avirtual machine deployed in a multi-user network). For example, due tothe speed of non-persistent memory, some approaches rely onnon-persistent memory to provision memory resources for virtual machinesdeployed in a multi-user network. However, in such approaches, costs canbe become an issue due to non-persistent memory generally being moreexpensive than persistent memory (e.g., the persistent memory device216).

In contrast, as described in more detail below, embodiments herein canallow for at least some data that is stored in the non-persistent memorydevice 230 to be stored in the persistent memory device 216. This canallow for additional memory resources to be provided to a computingsystem 201, such as a multi-user network, at a lower cost thanapproaches that rely on non-persistent memory for user data storage.

The computing system 201 can include a memory management component 214,which can be communicatively coupled to the non-persistent memory device230 and/or the interface 208. In some embodiments, the memory managementcomponent 214 can be a, input/output memory management unit (IO MMU)that can communicatively couple a direct memory access bus such as theinterface 208 to the non-persistent memory device 230. Embodiments arenot so limited, however, and the memory management component 214 can beother types of memory management hardware that facilitates communicationbetween the interface 208 and the non-persistent memory device 230.

The memory management component 214 can map device-visible virtualaddresses to physical addresses. For example, the memory managementcomponent 214 can map virtual addresses associated with the I/O device210 to physical addresses in the non-persistent memory device 230 and/orthe persistent memory device 216. In some embodiments, mapping thevirtual entries associated with the I/O device 210 can be facilitated bythe read buffer, write buffer, and/or I/O access buffer illustrated inFIG. 1 , herein.

In some embodiments, the memory management component 214 can read avirtual address associated with the I/O device 210 and/or map thevirtual address to a physical address in the non-persistent memorydevice 230 or to an address in the hierarchical memory component 204. Inembodiments in which the memory management component 214 maps thevirtual I/O device 210 address to an address in the hierarchical memorycomponent 204, the memory management component 214 can redirect a readrequest (or a write request) received from the I/O device 210 to thehierarchical memory component 204, which can store the virtual addressinformation associated with the I/O device 210 read or write request inan address register (e.g., the address register 206-1, 206-2, . . . ,206-N) of the hierarchical memory component 204. In some embodiments,the address register 206-N can be a particular base address register ofthe hierarchical memory component 204, such as a BAR4 address register.

The redirected read (or write) request can be transferred from thememory management component 214 to the hierarchical memory component 204via the interface 208. In some embodiments, the interface 208 can be aPCIe interface and can therefore pass information between the memorymanagement component 214 and the hierarchical memory component 204according to PCIe protocols. Embodiments are not so limited, however,and in some embodiments the interface 208 can be an interface or busthat functions according to another suitable protocol.

After the virtual NIC address is stored in the hierarchical memorycomponent 204, the data corresponding to the virtual NIC address can bewritten to the persistent memory device 216. For example, the datacorresponding to the virtual NIC address stored in the hierarchicalmemory component 204 can be stored in a physical address location of thepersistent memory device 216. In some embodiments, transferring the datato and/or from the persistent memory device 216 can be facilitated by ahypervisor, as described in connection with FIGS. 3-5 , herein.

When the data is requested by, for example, a host computing device,such as a virtual machine deployed in the computing system 201, therequest can be redirected from the I/O device 210, by the memorymanagement component 214, to the hierarchical memory component 204.Because the virtual NIC address corresponding to the physical locationof the data in the persistent memory device 216 is stored in the addressregister 206-N of the hierarchical memory component 204, thehierarchical memory component 204 can facilitate retrieval of the datafrom the persistent memory device 216, in connection with a hypervisor,as described in more detail in connection with FIGS. 3-5 , herein.

In some embodiments, when data that has been stored in the persistentmemory device 216 is transferred out of the persistent memory device 216(e.g., when data that has been stored in the persistent memory device216 is requested by a host computing device), the data may betransferred to the intermediate memory component 220 and/or thenon-persistent memory device 230 prior to being provided to the hostcomputing device. For example, because data transferred to the hostcomputing device may be transferred in a deterministic fashion (e.g.,via a DDR interface), the data may be transferred temporarily to amemory that operates using a DDR bus, such as the intermediate memorycomponent 220 and/or the non-persistent memory device 230, prior to adata request being fulfilled.

FIG. 3 is another functional block diagram in the form of a computingsystem including a hierarchical memory component in accordance with anumber of embodiments of the present disclosure. As shown in FIG. 3 ,the computing system 301 can include a hierarchical memory component304, which can be analogous to the hierarchical memory component 104/204illustrated in FIGS. 1 and 2 . In addition, the computing system 301 caninclude an I/O device 310, a persistent memory device 316, anon-persistent memory device 330, an intermediate memory component 320,a memory management component 314, and a hypervisor 312.

In some embodiments, the computing system 301 can be a multi-usernetwork, such as a software defined data center, cloud computingenvironment, etc. In such embodiments, the computing system can beconfigured to have one or more virtual machines 317 running thereon. Forexample, in some embodiments, one or more virtual machines 317 can bedeployed on the hypervisor 312 and can be accessed by users of themulti-user network.

The I/O device 310, the persistent memory device 316, the non-persistentmemory device 330, the intermediate memory component 320, and the memorymanagement component 314 can be analogous to the I/O device 210, thepersistent memory device 216, the non-persistent memory device 230, theintermediate memory component 220, and the memory management component214 illustrated in FIG. 2 . Communication between the logic circuitry304, the I/O device 310 and the persistent memory device 316, thenon-persistent memory device 330, the hypervisor 312, and the memorymanagement component 314 may be facilitated via an interface 308, whichmay be analogous to the interface 208 illustrated in FIG. 2 .

As described above in connection with FIG. 2 , the memory managementcomponent 314 can cause a read request or a write request associatedwith the I/O device 310 to be redirected to the hierarchical memorycomponent 304. The hierarchical memory component 304 can generate and/orstore a logical address corresponding to the requested data. Asdescribed above, the hierarchical memory component 304 can store thelogical address corresponding to the requested data in a base addressregister, such as the address register 306-N of the hierarchical memorycomponent 304.

As shown in FIG. 3 , the hypervisor 312 can be in communication with thehierarchical memory component 304 and/or the I/O device 310 via theinterface 308. The hypervisor 312 can transmit data to and/or from thehierarchical memory component 304 via a NIC access component (e.g., theNIC access component 107 illustrated in FIG. 1 ) of the hierarchicalmemory component 304. In addition, the hypervisor 312 can be incommunication with the persistent memory device 316, the non-persistentmemory device 330, the intermediate memory component 320, and the memorymanagement component 314. The hypervisor can be configured to executespecialized instructions to perform operations and/or tasks describedherein.

For example, the hypervisor 312 can execute instructions to monitor datatraffic and data traffic patterns to determine whether data should bestored in the non-persistent memory device 330 or if the data should betransferred to the persistent memory device 316. That is, in someembodiments, the hypervisor 312 can execute instructions to learn userdata request patterns over time and selectively store portions of thedata in the non-persistent memory device 330 or the persistent memorydevice 316 based on the patterns.

For example, data can be stored in the non-persistent memory device 330or in the persistent memory device 316 based on a type of the data. Insome embodiments, type can refer to a file type, such as a photograph, adocument, an audio file, an application file, etc. A determinationregarding the location to store such data may be made on based onparticular user data request patterns. For example, a first user may bemore likely to access documents than photographs at a given moment whilea second user may exhibit the opposite behavior.

In some embodiments, for instance, data that is accessed more frequentlycan be stored in the non-persistent memory device 330 while data that isaccessed less frequently can be stored in the persistent memory device316. Stated differently, in some embodiments, data can be stored in thenon-persistent memory device 330 when past (e.g., historical) requestfrequency exceeds a frequency threshold, and data can be stored in thepersistent memory device 316 when past request frequency exceed aninfrequency threshold. In some embodiments, a frequency threshold and aninfrequency threshold can be a same threshold (e.g., a same numericalthreshold). In such embodiments, a frequency below that thresholdexceeds the infrequency threshold and a frequency above that thresholdexceeds the frequency threshold. Such thresholds can be determined basedon a particular time period, for instance, which can be adjustedaccording to data traffic and/or data patterns.

Because a user may access recently used or viewed data more often thandata that has been used less recently or viewed less recently, thehypervisor can execute specialized instructions to cause the data thathas been used or viewed less recently to be stored in the persistentmemory device 316 and/or cause the data that has been accessed or viewedmore recently in the non-persistent memory device 330. In a non-limitingexample, a user may view photographs on social media that have beentaken recently (e.g., within a week, etc.) more often than photographsthat have been taken less recently (e.g., a month ago, a year ago,etc.). Based on this information, the hypervisor 312 can executespecialized instructions to cause the photographs that were viewed ortaken less recently to be stored in the persistent memory device 316,thereby reducing an amount of data that is stored in the non-persistentmemory device 330. Stated differently, in some embodiments, data can bestored in the persistent memory device 316 when a past request (e.g., amost recent request) for that data exceeds a disuse threshold (e.g., afirst historical time instance), and data can be stored in thenon-persistent memory device 330 when a past request for that dataexceeds a recency threshold (e.g., a second historical time instance).In some embodiments, a disuse threshold and a recency threshold can be asame threshold (e.g., a same historical time instance). In suchembodiments, a past request made before that threshold time instanceexceeds the disuse threshold and a past request made after thatthreshold time instance exceeds the recency threshold. Such thresholdscan be determined based on a particular time period, for instance, whichcan be adjusted according to data traffic and/or data patterns.

Executing instructions to learn user data request patterns over time andselectively storing portions of the data in the non-persistent memorydevice 330 or the persistent memory device 316 based on the patterns canreduce an overall amount of non-persistent memory that is necessary toprovision the computing system 301, thereby reducing costs and allowingfor access to the non-persistent memory device 330 to more users.

In operation, the computing system 301 can be configured to intercept adata request from the I/O device 310 and redirect the request to thehierarchical memory component 304. In some embodiments, the hypervisor312 can control whether data corresponding to the data request is to bestored in (or retrieved from) the non-persistent memory device 330 or inthe persistent memory device 316. For example, the hypervisor 312 canexecute instructions to selectively control if the data is stored in (orretrieved from) the persistent memory device 316 or the non-persistentmemory device 330.

As part of controlling whether the data is stored in (or retrieved from)the persistent memory device 316 and/or the non-persistent memory device330, the hypervisor 312 can cause the memory management component 314 tomap logical addresses associated with the data to be redirected to thehierarchical memory component 304 and stored in the address registers306 of the hierarchical memory component 304. For example, thehypervisor 312 can execute instructions to control read and writerequests involving the data to be selectively redirected to thehierarchical memory component 304 via the memory management component314.

The memory management component 314 can map contiguous virtual addressesto underlying fragmented physical addresses. Accordingly, in someembodiments, the memory management component 314 can allow for virtualaddresses to be mapped to physical addresses without the requirementthat the physical addresses are contiguous. Further, in someembodiments, the memory management component 314 can allow for devicesthat do not support memory addresses long enough to address theircorresponding physical memory space to be addressed in the memorymanagement component 314.

Due to the non-deterministic nature of data transfer associated with thepersistent memory device 316, the hierarchical memory component 304 can,in some embodiments, be configured to inform the computing system 301that a delay in transferring the data to or from the persistent memorydevice 316 may be incurred. As part of initializing the delay, thehierarchical memory component 304 can provide page fault handling forthe computing system 301 when a data request is redirected to thehierarchical memory component 304. In some embodiments, the hierarchicalmemory component 304 can generate and assert an interrupt to thehypervisor 312 to initiate an operation to transfer data into or out ofthe persistent memory device 316. For example, due to thenon-deterministic nature of data retrieval and storage associated withthe persistent memory device 316, the hierarchical memory component 304can generate a hypervisor interrupt 315 when a transfer of the data thatis stored in the persistent memory device 316 is requested.

In response to the page fault interrupt generated by the hierarchicalmemory component 304, the hypervisor 312 can retrieve informationcorresponding to the data from the hierarchical memory component 304.For example, the hypervisor 312 can receive NIC access data from thehierarchical memory component, which can include logical to physicaladdress mappings corresponding to the data that are stored in theaddress registers 306 of the hierarchical memory component 304.

Once the data has been stored in the persistent memory device 316, aportion of the non-persistent memory device 330 (e.g., a page, a block,etc.) can be marked as inaccessible by the hierarchical memory component304 so that the computing system 301 does not attempt to access the datafrom the non-persistent memory device 330. This can allow a data requestto be intercepted with a page fault, which can be generated by thehierarchical memory component 304 and asserted to the hypervisor 312when the data that has been stored in the persistent memory device 316is requested by the I/O device 310.

In contrast to approaches in which a page fault exception is raised inresponse to an application requesting access to a page of memory that isnot mapped by a memory management unit (e.g., the memory managementcomponent 314), in embodiments of the present disclosure, the page faultdescribed above can be generated by the hierarchical memory component304 in response to the data being mapped in the memory managementcomponent 314 to the hierarchical memory component 304, which, in turnmaps the data to the persistent memory device 316.

In some embodiments, the intermediate memory component 320 can be usedto buffer data that is stored in the persistent memory device 316 inresponse to a data request initiated by the I/O device 310. In contrastto the persistent memory device 316, which may pass data via a PCIeinterface, the intermediate memory component 320 may employ a DDRinterface to pass data. Accordingly, in some embodiments, theintermediate memory component 320 may operate in a deterministicfashion. For example, in some embodiments, data requested that is storedin the persistent memory device 316 can be temporarily transferred fromthe persistent memory device 316 to the intermediate memory component320 and subsequently transferred to a host computing device via a DDRinterface coupling the intermediate memory component 320 to the I/Odevice 310.

In some embodiments, the intermediate memory component can comprise adiscrete memory component (e.g., an SRAM cache) deployed in thecomputing system 301. However, embodiments are not so limited and, insome embodiments, the intermediate memory component 320 can be a portionof the non-persistent memory device 330 that can be allocated for use intransferring data from the persistent memory device 316 in response to adata request.

In a non-limiting example, memory management circuitry (e.g., the memorymanagement component 314) can be coupled to logic circuitry (e.g., thehierarchical memory component 304). The memory management circuitry canbe configured to receive a request to write data having a correspondingvirtual network interface controller address associated therewith to anon-persistent memory device (e.g., the non-persistent memory device330). The memory management circuitry can be further configured toredirect the request to write the data to the logic circuitry, based, atleast in part, on characteristics of the data. The characteristics ofthe data can include how frequently the data is requested or accessed,an amount of time that has transpired since the data was last accessedor requested, a type of data (e.g., whether the data corresponds to aparticular file type such as a photograph, a document, an audio file, anapplication file, etc.), among others.

In some embodiments, the memory management circuitry can be configuredto redirect the request to write the logic circuitry based on commandsgenerated by and/or instructions executed by the hypervisor 312. Forexample, as described above, the hypervisor 312 can execute instructionsto control whether data corresponding to a data request (e.g., a datarequest generated by the I/O device 310) is to be stored in thepersistent memory device 316 or the non-persistent memory device 330.

In some embodiments, the hypervisor 312 can facilitate redirection ofthe request by writing addresses (e.g., logical addresses) to the memorymanagement circuitry. For example, if the hypervisor 312 determines thatdata corresponding to a particular data request is to be stored in (orretrieved from) the persistent memory device 316, the hypervisor 312 cancause an address corresponding to redirection of the request to bestored by the memory management circuitry such that the data request isredirected to the logic circuitry.

Upon receipt of the redirected request, the logic circuitry can beconfigured to generate an address corresponding to the data in responseto receipt of the redirected request and/or store the address in anaddress register 306 within the logic circuitry. In some embodiments,wherein the logic circuitry can be configured to associate an indicationwith the data that indicates that the data is inaccessible to thenon-persistent memory device 330 based on receipt of the redirectedrequest.

The logic circuitry can be configured to cause the data to be written toa persistent memory device (e.g., the persistent memory device 316)based, at least in part, on receipt of the redirected request. In someembodiments, the logic circuitry can be configured to generate aninterrupt signal and assert the interrupt signal to a hypervisor (e.g.,the hypervisor 312) coupled to the logic circuitry as part of causingthe data to be written to the persistent memory device 316. As describedabove, the persistent memory device 316 can comprise a 3D XP memorydevice, an array of self-selecting memory cells, a NAND memory device,or other suitable persistent memory, or combinations thereof.

In some embodiments, the logic circuitry can be configured to receive aredirected request from the memory management circuitry to retrieve thedata from the persistent memory device 316, transfer a request toretrieve the data from the persistent memory device 316 to a hypervisor312 coupled to the logic circuitry, and/or assert an interrupt signal tothe hypervisor 312 as part of the request to retrieve the data from thepersistent memory device 316. The hypervisor 312 can be configured toretrieve the data from the persistent memory device 316 and/or transferthe data to the non-persistent memory device 330. Once the data has beenretrieved from the persistent memory device 316, the hypervisor 312 canbe configured to cause an updated address associated with the data to betransferred to the memory management circuitry 314.

In another non-limiting example, the computing system 301 can be amulti-user network such as a software-defined data center, a cloudcomputing environment, etc. The multi-user network can include a pool ofcomputing resources that include a non-persistent memory device 330 anda persistent memory device 316. The multi-user network can furtherinclude an interface 308 coupled to logic circuitry (e.g., thehierarchical memory component 304) comprising a plurality of addressregisters 306. In some embodiments, the multi-user network can furtherinclude a hypervisor 312 coupled to the interface 308.

The hypervisor 312 can be configured to receive a request to access datacorresponding to the non-persistent memory component 330, determine thatthe data is stored in the persistent memory device 316, and cause therequest to access the data to be redirected to the logic circuitry. Therequest to access the data can be a request to read the data from thepersistent memory device or the non-persistent memory device or arequest to write the data to the persistent memory device or thenon-persistent memory device.

In some embodiments, the logic circuitry can be configured to transfer arequest to the hypervisor 312 to access the data from the persistentmemory device 316 in response to the determination that the data isstored in the persistent memory device 316. The logic circuitry can beconfigured to assert an interrupt to the hypervisor as part of therequest to the hypervisor 312 to access the data corresponding to thepersistent memory device 316.

The hypervisor 312 can be configured to cause the data to be accessedusing the persistent memory device 316 based on the request receivedfrom the logic circuitry. As described above, the persistent memorydevice 316 can comprise a resistance variable memory device such as aresistive memory, a phase change memory, an array of self-selectingmemory cells, or combinations thereof. In some embodiments, thehypervisor 312 can be configured to cause the data to be transferred toa non-persistent memory device 330 as part of causing the data to beaccessed using the persistent memory device 316.

The hypervisor 312 can be further configured to update informationstored in a memory management component 314 associated with themulti-user network in response to causing the data to be accessed usingthe persistent memory device 316. For example, the hypervisor 312 can beconfigured to cause updated virtual addresses corresponding to the datato be stored in the memory management component 314.

The multi-user network can, in some embodiments, include an I/O device310 coupled to the logic circuitry. In such embodiments, the logiccircuitry can be configured to send a notification to the I/O device 310in response to the hypervisor 312 causing the data to be accessed usingthe persistent memory device 316.

FIG. 4 is a flow diagram 440 representing a data read operation inaccordance with a number of embodiments of the present disclosure. Atblock 441, an I/O device, such as the I/O device 210/310 illustrated inFIGS. 2 and 3 can initiate a read operation using an addresscorresponding to a data request. In some embodiments, the address can bea physical address, such as a virtual machine physical address. The datarequest can include a request to read data associated with a particularaddress that corresponds to a logical address in which the data isstored. The physical address can correspond to a location in apersistent memory device (e.g., the persistent memory device 216/316illustrated in FIGS. 2 and 3 , herein) or a location in a non-persistentmemory device (e.g., the non-persistent memory device 230/330illustrated in FIGS. 2 and 3 , herein).

If the data is stored in the non-persistent memory device, the data maybe retrieved, and the data request can be fulfilled. However, if thedata is stored in the persistent memory device (e.g., if the physicaladdress of the data corresponds to a location in the persistent memorydevice), at block 442 a memory management component (e.g., the memorymanagement component 214/314 illustrated in FIGS. 2 and 3 , herein) canredirect the data request to a hierarchical memory component (e.g., thehierarchical memory component 104/204/304 illustrated in FIGS. 1-3 ,herein). As described above, the data request can be redirected based oninformation (e.g., a command or instructions executed) by a hypervisor(e.g., the hypervisor 312 illustrated in FIG. 3 , herein).

At block 443, the hierarchical memory component can receive addressregister access information corresponding to the data request. In someembodiments, the address register access information can correspond to alocation in an address register (e.g., the address registers 106/206/306illustrated in FIGS. 1-3 , herein). For example, the address registeraccess information can correspond to a location in an address registerin the hierarchical memory component in which a logical addresscorresponding to a physical address in the persistent memory device inwhich the data is stored.

The hierarchical memory component can, at block 444, generate ahypervisor interrupt. For example, as described above in connection withFIG. 3 , once the hierarchical memory component has received theredirected data request from the memory management component, thehierarchical memory component can generate an interrupt and assert theinterrupt on a hypervisor (e.g., the hypervisor 312 illustrated in FIG.3 , herein). In some embodiments, the interrupt can be a signal that isasserted on the hypervisor to inform the hypervisor that an event needsimmediate attention. For example, the interrupt signal can be assertedon the hypervisor to cause the hypervisor to interrupt instructions thatare being currently executed and instead execute instructions associatedwith gathering the address register access information at block 445.

At block 445, the hypervisor can gather the address register accessinformation from the hierarchical memory component. For example, thehypervisor can receive logical address information from the hierarchicalmemory component that corresponds to the physical address of therequested data. The logical address information can be stored in thehierarchical memory component in an address register (e.g., a baseaddress register) of the hierarchical memory component, such as theaddress register(s) 106/206/306 illustrated in FIGS. 1-3 , herein.

At block 446, the hypervisor can determine a physical location of therequested data. For example, based on the address register accessinformation and, hence, the logical address associated with the datagathered from the hierarchical memory component, the hypervisor candetermine the physical location of the data stored in the persistentmemory device.

At block 447, the hypervisor can read the data corresponding to theaddress register access information. That is, in some embodiments, thehypervisor can cause the requested data to be read (e.g., retrieved)from the persistent memory device.

At block 448, the hypervisor can cause the data to be transferred to anon-persistent memory device. In some embodiments, the non-persistentmemory device can be the non-persistent memory device 230/330illustrated in FIGS. 2 and 3 , herein, however embodiments are not solimited and in some embodiments, the hypervisor can cause the data to betransferred to an intermediate memory component, such as theintermediate memory component 220/320 illustrated in FIGS. 2 and 3 ,herein.

At block 449, the hypervisor can write I/O device data corresponding tothe requested data to the hierarchical memory component. The I/O devicedata can be stored in an address register of the hierarchical memorycomponent, as described above.

At block 450, the hierarchical memory component can complete the dataread transaction. For example, the hierarchical memory component cantransfer a command to the I/O device to inform the I/O device that thedata read request has been fulfilled and the data will be transferredvia a deterministic interface to fulfill the data read request.

At block 451, the hypervisor can update the memory management componentto direct an I/O device address to the non-persistent memory device. Forexample, since the data was transferred from the persistent memorydevice to a non-persistent memory device (e.g., a non-persistent memorydevice and/or an intermediate memory component) at block 450, thehypervisor can update the memory management component such that anaddress corresponding to the data requested maps to the non-persistentmemory device. In some embodiments, the address can be a physicaladdress such as a virtual machine physical address.

At block 452, the hypervisor can record which memory was used to satisfythe data request. For example, the hypervisor can record that the datahad been stored in the persistent memory device at the time the datarequest was received from the I/O device. In some embodiments, thehypervisor can use the information over time to selectively direct datawrites to the persistent memory device or the non-persistent memorydevice.

FIG. 5 is a flow diagram 560 representing a data write operation inaccordance with a number of embodiments of the present disclosure. Atblock 561, an I/O device, such as the I/O device 210/310 illustrated inFIGS. 2 and 3 can initiate a write operation using an addresscorresponding to a data write request. The address can be a physicaladdress, such as a virtual-machine physical address. The data writerequest can include a request to write data associated with a particularvirtual address that corresponds to a logical address in which the datais to be stored. The physical address can correspond to a location in apersistent memory device (e.g., the persistent memory device 216/316illustrated in FIGS. 2 and 3 , herein) or a location in a non-persistentmemory device (e.g., the non-persistent memory device 230/330illustrated in FIGS. 2 and 3 , herein.

If the data is to be stored in the non-persistent memory device, thedata may be written to the non-persistent memory device and the datawrite request can be fulfilled. However, if the data is to be stored inthe persistent memory device, at block 562 a memory management component(e.g., the memory management component 214/314 illustrated in FIGS. 2and 3 , herein) can redirect the data write request to a hierarchicalmemory component (e.g., the hierarchical memory component 104/204/304illustrated in FIGS. 1-3 , herein). As described above, the data requestcan be redirected based on information (e.g., a command or instructionsexecuted) by a hypervisor (e.g., the hypervisor 312 illustrated in FIG.3 , herein).

At block 563, the hierarchical memory component can receive addressregister access information corresponding to the data write request. Insome embodiments, the address register access information can correspondto a location in an address register (e.g., the address registers106/206/306 illustrated in FIGS. 1-3 , herein). For example, the addressregister access information can correspond to a location in an addressregister in the hierarchical memory component in which a logical addresscorresponding to a physical address in the persistent memory device inwhich the data is to be stored.

The hierarchical memory component can, at block 564, generate ahypervisor interrupt. For example, as described above in connection withFIG. 3 , once the hierarchical memory component has received theredirected data write request from the memory management component, thehierarchical memory component can generate an interrupt and assert theinterrupt on a hypervisor (e.g., the hypervisor 312 illustrated in FIG.3 , herein).

At block 565, the hypervisor can gather the address register accessinformation from the hierarchical memory component. For example, thehypervisor can receive logical address information from the hierarchicalmemory component that corresponds to a physical address in which thedata is to be stored.

At block 566, the hypervisor can optionally write the data (or cause thedata to be written) to the persistent memory device. For example, basedon the redirected data write request, the hypervisor can determine thatthe data is to be written to the persistent memory device and cause thedata to be written to the persistent memory device. In embodiments inwhich block 566 is optionally performed, the data can be intermediatelywritten to the non-persistent memory device. In addition, I/O devicedata corresponding to the data can be optionally written to thenon-persistent memory device as part of writing the data to thenon-persistent memory device.

Optionally, at block 567, the hypervisor can write the data (or causethe data to be written) to the non-persistent memory device. In someembodiments, the hypervisor can write the data to the non-persistentmemory device such that the data can be retrieved via a deterministicinterface or bus in the event a read request corresponding the data isreceived.

At block 568, the hypervisor can update the memory management componentto direct I/O device virtual addresses to the non-persistent memorydevice. For example, if the data is written to the non-persistent memorydevice at block 567, the hypervisor can, at block 568, update virtualaddresses stored by the memory management component such that thevirtual addresses associated with the data and stored by the memorymanagement component are mapped to physical addresses in thenon-persistent memory device in which the data is stored.

FIG. 6 is a flow diagram representing an example method 670 for ahierarchal memory system in accordance with a number of embodiments ofthe present disclosure. At block 672, the method 670 can includereceiving an interrupt message by a hypervisor, the interrupt messagegenerated by a hierarchical memory component responsive to receiving aread request initiated by an input/output (I/O) device. The hypervisorcan be analogous to the hypervisor 312 illustrated in FIG. 3 , herein,while the hierarchical memory component and the I/O device can berespectively analogous to the hierarchical memory component 104/204/304illustrated in FIGS. 1-3 , herein, and the I/O device 210/310illustrated in FIGS. 2 and 3 , herein.

At block 674, the method 670 can include gathering, by the hypervisor,address register access information from the hierarchical memorycomponent. The address register access information can correspond to alocation in an address register (e.g., the address registers 106/206/306illustrated in FIGS. 1-3 , herein).

At block 676, the method 670 can include determining, by the hypervisor,a physical location of data associated with the read request. Forexample, based on the address register access information and, hence,the logical address associated with the data gathered from thehierarchal memory component, the hypervisor can determine the physicallocation of the data stored in the persistent memory device.

The method 670 can include reading, by the hypervisor, the dataassociated with the read request and corresponding to the addressregister access information. In some embodiments, the method 670 caninclude executing the read request responsive to the data being storedin a non-persistent memory device. In some embodiments, the method 670can include storing the data in a non-persistent memory deviceresponsive to the data being stored in a persistent memory device. Insome embodiments, the method 670 can include transferring, via thehypervisor, the data to a non-persistent memory device.

In some embodiments, the method 670 can include writing, via thehypervisor, data associated with the I/O device to the hierarchicalmemory component. In some embodiments, the method 670 can includeupdating a memory management component to redirect read requests for theaddress to a non-persistent memory device responsive to the data beingstored in a persistent memory device. In some embodiments, the method670 can include recording a memory device type the hypervisor used torespond to the read request. For example, the memory device type caninclude a first type (e.g., a persistent memory device) or a second type(e.g., a non-persistent memory device).

FIG. 7 is another flow diagram representing an example method 780 for ahierarchal memory system in accordance with a number of embodiments ofthe present disclosure. At block 782, the method 780 can includereceiving an interrupt message by a hypervisor, the interrupt messagegenerated by a hierarchical memory component responsive to receiving arequest initiated by an input/output (I/O) device to write data to avirtual address. As described herein, for example, an address register(e.g., address register 106-N) can be configured as a virtual addressspace that can store logical addresses that correspond to physicalmemory locations (e.g., in a memory device) in which data is stored. Thehypervisor can be analogous to the hypervisor 312 illustrated in FIG. 3, herein, while the hierarchical memory component and the I/O device canbe respectively analogous to the hierarchical memory component104/204/304 illustrated in FIGS. 1-3 , herein, and the I/O device210/310 illustrated in FIGS. 2 and 3 , herein.

At block 784, the method 780 can include gathering, by the hypervisor,I/O device access information from the hierarchical memory component.The I/O device access information can be included in an I/O accesscomponent (e.g., the I/O access component 107), illustrated in FIG. 1 ,herein. The I/O access component can store data corresponding to accessto a component external to the hierarchical memory component 104, suchas an I/O device (e.g., I/O device 210/310 illustrated in FIGS. 2 and 3, herein). The I/O access component can store data corresponding toaddresses of the I/O device, which can be used to read and/or write datato and from the I/O device. The I/O device access information caninclude physical I/O device access information and/or virtual I/O deviceaccess information.

At block 786, the method 780 can include writing data, by thehypervisor, to a location selected based in part on the gathered I/Odevice access information. The location can correspond to a physicaladdress, such as a virtual-machine physical address, for instance. Thelocation can correspond to a location in a persistent memory device(e.g., the persistent memory device 216/316 illustrated in FIGS. 2 and 3, herein) or a location in a non-persistent memory device (e.g., thenon-persistent memory device 230/330 illustrated in FIGS. 2 and 3 ,herein.

In some embodiments, the method 780 can include writing the data, by thehypervisor, to a non-persistent memory device based in part on a pastrequest frequency associated with the data exceeding a frequencythreshold. In some embodiments, the method 780 can include writing thedata, by the hypervisor, to a persistent memory device based in part ona past request frequency associated with the data exceeding aninfrequency threshold. In some embodiments, the method 780 can includewriting the data, by the hypervisor, to a persistent memory device basedin part on a past request associated with the data exceeding a recencythreshold. In some embodiments, the method 780 can include writing thedata, by the hypervisor, to a non-persistent memory device based in parton a past request associated with the data not exceeding a recencythreshold

Although specific embodiments have been illustrated and describedherein, those of ordinary skill in the art will appreciate that anarrangement calculated to achieve the same results can be substitutedfor the specific embodiments shown. This disclosure is intended to coveradaptations or variations of one or more embodiments of the presentdisclosure. It is to be understood that the above description has beenmade in an illustrative fashion, and not a restrictive one. Combinationof the above embodiments, and other embodiments not specificallydescribed herein will be apparent to those of skill in the art uponreviewing the above description. The scope of the one or moreembodiments of the present disclosure includes other applications inwhich the above structures and processes are used. Therefore, the scopeof one or more embodiments of the present disclosure should bedetermined with reference to the appended claims, along with the fullrange of equivalents to which such claims are entitled.

In the foregoing Detailed Description, some features are groupedtogether in a single embodiment for the purpose of streamlining thedisclosure. This method of disclosure is not to be interpreted asreflecting an intention that the disclosed embodiments of the presentdisclosure have to use more features than are expressly recited in eachclaim. Rather, as the following claims reflect, inventive subject matterlies in less than all features of a single disclosed embodiment. Thus,the following claims are hereby incorporated into the DetailedDescription, with each claim standing on its own as a separateembodiment.

What is claimed is:
 1. A method, comprising: receiving, from a statemachine, an interrupt message by a base address register of logiccircuitry coupled to a plurality of memory media types each havingdifferent latency or persistence characteristics, or both, wherein theinterrupt message is generated responsive to receiving a read requestinitiated by an input/output (I/O) device; receiving, from the logiccircuitry, the interrupt message by a hypervisor; gathering, by thehypervisor, address register access information from the logiccircuitry; and determining, by the hypervisor, a physical location ofdata associated with the read request.
 2. The method of claim 1, whereinthe method includes reading, by the hypervisor, the data associated withthe read request and corresponding to the address register accessinformation.
 3. The method of claim 1, wherein the address is a physicaladdress location of the data.
 4. The method of claim 1, wherein themethod includes executing the read request responsive to the data beingstored in a non-persistent component coupled to the logic circuitry. 5.The method of claim 4, wherein the method includes storing the data inthe non-persistent component responsive to the data being stored in apersistent component coupled to the logic circuitry.
 6. The method ofclaim 1, wherein the method includes transferring, via the hypervisor,the data to a non-persistent component coupled to the logic circuitry.7. The method of claim 1, wherein the method includes writing, via thehypervisor, data associated with the I/O device to the logic circuitry.8. The method of claim 1, wherein the method includes updating a memorymanagement component of the logic circuitry to redirect read requestsfor the address to a non-persistent memory component coupled to thelogic circuitry responsive to the data being stored in a persistentcomponent coupled to the logic circuitry.
 9. The method of claim 1,wherein the method includes recording a memory device type thehypervisor used to respond to the read request.
 10. An apparatus,comprising: an input/output (I/O) component configured to initiate aread request; a state machine configured to receive the read requestinitiated by the I/O component and generate an interrupt message; a baseaddress register of logic circuitry couplable to a plurality of memorymedia types each having different latency or persistencecharacteristics, the logic circuitry configured to receive the interruptmessage; and a hypervisor, configured to: receive the interrupt messagefrom the logic circuitry; gather address register access informationfrom the base address register of the logic circuitry responsive toreceiving the interrupt message; determine a physical location of dataassociated with the read request; and read the data associated with theread request and corresponding to the address register accessinformation.
 11. The apparatus of claim 10, wherein the hypervisor isconfigured to cause the data to be transferred to a non-persistentcomponent couplable to the logic circuitry.
 12. The apparatus of claim10, wherein the hypervisor is configured to cause the data to betransferred to an intermediate component couplable to the logiccircuitry.
 13. The apparatus of claim 10, wherein the apparatus includesa memory management component, and wherein the hypervisor is configuredto update the memory management component to redirect read requests forthe address to a non-persistent component couplable to the logiccircuitry responsive to the data being stored in a persistent componentcouplable to the logic circuitry.
 14. The apparatus of claim 13, whereinthe address is a virtual machine physical address.
 15. An apparatus,comprising: an input/output (I/O) component configured to initiate awrite request to write data to a virtual address; a state machineconfigured to receive the write request initiated by the I/O componentand generate an interrupt message; a base address register of acomponent that comprises a plurality of memory media types each havingdifferent latency or persistence characteristics, the componentconfigured to receive the interrupt message; and a hypervisor,configured to: receive an interrupt message from the component; gatherI/O device access information from the component; and write data to alocation selected based in part on the gathered I/O device accessinformation.
 16. The apparatus of claim 15, wherein the hypervisor isconfigured to write the data to one of: a persistent component of thememory device and a non-persistent component of the memory device basedin part on a recency of an access of the data.
 17. The apparatus ofclaim 16, wherein the access of the data comprises a most recent accessof the data.
 18. The apparatus of claim 15, wherein the hypervisor isconfigured to write the data to one of: a persistent component of thememory device and a non-persistent component of the memory device basedin part on a type of the data.
 19. The apparatus of claim 15, whereinthe hypervisor is configured to write the data to a non-persistentcomponent of the memory device responsive to a determination that thedata has been accessed in excess of a particular frequency.
 20. Theapparatus of claim 15, wherein the hypervisor is configured to write thedata to a persistent component of the memory device based in part on arequest associated with the data exceeding a disuse threshold.